The Lacrimal Bone
The lacrimal bone is a paired facial bone that makes up the most anterior part of the medial wall of the orbit. It is the size and shape of a fingernail and thus the smallest bone of the skull. “Lacrima” is latin for “tear”, so the name of the bone corresponds with its relation to the nearby lacrimal structures.
After this article, it will be clear that the function of the lacrimal bone is to support parts of the lacrimal apparatus, especially the lacrimal sac and lacrimal canaculi, while at the same time, it participates in forming of the medial wall of the orbit.
Lateral surface - houses lacrimal sac and nasolacrimal duct; participates in forming the medial orbital wall
Medial surface - participates in forming the middle nasal meatus and encloses some ethmoidal air cells
Anterior - articulation with the frontal process of maxilla
Posterior - articulation with the orbital lamina of the ethmoid bone
Superior - articulation with the frontal bone
Inferior - articulates with the orbital plate of the maxilla and the inferior nasal concha
|Clinical relations||Fracture, lacrimal canaliculi obstruction|
This article will discuss anatomical landmarks of the lacrimal bone.
The lacrimal bone is both the smallest and the most fragile bone of the face. Anatomically, we can observe its four borders and two surfaces.
The lateral surface of the lacrimal bone faces towards the contents of the orbit, thus is often referred to as the orbital surface. The first notable feature of this surface is a vertical ridge called the posterior lacrimal crest. The crest divides the lateral surface of the bone into two portions: the anterior, which is related to the lacrimal sac and lacrimal canaliculi; and posterior, which is part of the posterior wall of the orbit.
Anterior to the posterior lacrimal crest is a longitudinally positioned groove called the lacrimal groove (or lacrimal sulcus). The inner margin of this sulcus unites with the frontal process of the maxilla and in this way forms the lacrimal fossa. The upper part of the lacrimal fossa houses the lacrimal sac, whereas the lower part contains the nasolacrimal duct.
Posterior to the posterior lacrimal crest is a smooth surface that participates in forming the medial wall of the orbit. The part of this smooth surface that is immediately behind the posterior lacrimal crest is the place of origin of the orbicularis oculi muscle.
This portion of the lateral surface also extends in the shape of a hook called the lacrimal hamulus and it articulates with the lacrimal tubercle of the maxilla. In this way, the lacrimal bone and the maxilla enclose the lacrimal canaliculus.
The medial surface of the lacrimal bone faces the nasal cavity, which is why it is also called the nasal surface. There is notable longitudinal furrow on this surface, which corresponds to the posterior lacrimal crest of the orbital surface.
Anterior to the furrow is a portion of the bone that forms part of the middle nasal meatus, whereas the part located posteriorly to the furrow articulates with the ethmoid bone, and in this way encloses some ethmoidal air cells.
The anterior border of the lacrimal bone articulates with the frontal process of the maxilla, whereas the posterior border articulates with the orbital lamina of the ethmoid bone.
The superior border articulates with the frontal bone, while the inferior border has complex relations since it is divided into two parts by the inferior edge of the posterior lacrimal crest. The part of the inferior border that is placed posteriorly to the posterior lacrimal crest articulates with the orbital plate of the maxilla, whereas the part located anteriorly extends downward. This extension is called the descending process and it articulates with the lacrimal process of the inferior nasal concha, and in that way participates in enclosing the bony canal for the nasolacrimal duct.
During intrauterine development, a cartilaginous membrane that covers the cartilaginous nasal capsule at the place where the lacrimal bone first develops. Around the 12th week of gestation, a single ossification center appears within this membrane, causing intramembranous ossification from a single ossification center, which subsequently leads into forming of the lacrimal bone.
It was mentioned before that the lacrimal bone is the most fragile facial bone. Fractures of this bone often causes obstruction of the nasolacrimal duct. This increases pressure in the duct, and can cause injury to its walls. Increased pressure within the duct presents with watery and irritated eyes because the tears cannot drain normally.